Hey Pal, You can replace the modifiers in the line 9 and 10 with protected and static respectively.
Make the constructor protected to make it visible to the SingleSub and you can replace protected to static in line 10 to make the code to compile, since in line 10 non-static create() is attempted to use in a static method getInstance(). either you can add static with protected in the line 10. but the ques is about replacing. Hence you can replace this two. to make you code to compile.